Precious metal incorporated into stable lattices like perovskites can be envisaged as an alternative catalysts to address deactivation problems. Here we report the barium cerate perovskite doped with varying amounts of Pt as catalysts for the water−gas shift reaction whereby ionic Pt is evidenced to be active. It is found that maximum CO conversion occurs above 325 °C and increases more than 2-fold after the first cycle. XPS analysis shows that after the first cycle, more ionic Pt species are present on the surface of the catalyst. X-ray and neutron diffraction studies also indicate the presence of oxygen vacancies that increases with increasing Pt substitution.
Oxygen
vacancies are suggested to play an important role in reactions
like water gas shift where the redox mechanism is crucial. Pt-doped
BaCeO3 perovskite, moderately active for water gas shift
reaction, is selected for further understanding the role of oxygen
vacancies, since perovskite lattice can tolerate and stabilize vacancies
facilitating an accurate quantification. Vacancies are created in
the system by systematic doping of increasing amounts of Y. Structure
and activity studies reveal that the 6% Y-substituted compound which
has the most symmetric B site coordination environment exhibits the
highest activity. Hence, it is not the extent of vacancies but their
structural characteristics which are found to be decisive. Symmetric
coordination around B ions facilitates water adsorption and dissociation
by lowering the energy barriers due to the creation of an isotropic
environment.
This work reports product composition and kinetics of the catalytic decomposition of methylal (dimethoxymethane, C 3 H 8 O 2 ), which is a good hydrogen vector. To the best of our knowledge, this is the first report on methylal reforming by decomposition over supported metal catalysts for fueling an internal combustion engine (ICE) while using the hot exhaust gases to heat the reactor. The decomposition activities of commercial Pt/Al 2 O 3 , Ni/Al 2 O 3 , and laboratorysynthesized Rh/Al 2 O 3 were investigated. While the activities of Pt and Ni catalysts were promising, Rh exhibits poor activity. Pt catalyst exhibits appreciable methylal conversion and yields primarily a mixture of H 2 , CO, and DME above 300 °C. Ni produces a mixture of H 2 , CO, and methane. Isothermal studies revealed that both catalysts undergo deactivation evident by an initial decline in H 2 and CO production rates while DME production was stable. Coke deposition was observed on both catalysts, but the TPO revealed 5 times more coke on Ni catalysts than on Pt at 300 °C. Since the deposited carbon is reactive in nature, a simple regeneration step at temperatures around 400 °C is sufficient to restore the activity. Based on the experimental results, a model in the form of two consecutive reactions, decomposition to methanol followed by reforming to DME + H 2 + CO, was developed for Pt, and the rate constants and activation energies were determined.
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